title: Effect of vitamin D replacement on hip structural geometry in adolescents: a randomized controlled trial.
abstract: BACKGROUND
  We have shown in a randomized controlled trial that vitamin D increases bone mass, lean mass and bone area in adolescent girls, but not boys. These increments may translate into improvements in bone geometry and therefore bone strength. This study investigated the impact of vitamin D on hip geometric dimensions from DXA-derived hip structural analyses in adolescents who participated in the trial.
  
  
  METHODS
  167 girls (mean age 13.1 years) and 171 boys (mean age 12.7 years) were randomly assigned to receive weekly placebo oil or vitamin D3, at doses of 1400 IU or 14,000 IU, in a double blind placebo-controlled 1-year trial. DXA images were obtained at baseline and one year, and hip images were analyzed using the hip structural analysis (HSA) software to derive parameters of bone geometry. These include outer diameter (OD), cross sectional area (CSA), section modulus (Z), and buckling ratio (BR) at the narrow neck (NN), intertrochanteric (IT), and shaft (S) regions. Analysis of Covariance (ANCOVA) was used to examine group differences for changes of bone structural parameters.
  
  
  RESULTS
  In the overall group of girls, vitamin D supplementation increased aBMD (7.9% and 6.8% in low and high doses, versus 4.2% in placebo) and reduced the BR of NN (6.1% and 2.4% in low and high doses, versus 1.9% in placebo). It also improved aBMD (7.9% and 5.2% versus 3.6%) and CSA (7.5% and 5.1% versus 4.1%) of the IT and OD of the S (2.4% and 2.5% versus 0.8% respectively). Significant changes in the OD and BR of the NN, in the overall group of girls remained, after adjusting for lean mass, and were unaffected with further adjustments for lifestyle, pubertal status, and height measures. Conversely, boys did not exhibit any significant changes in any parameters of interest. A dose effect was not detected and subgroup analyses revealed no beneficial effect of vitamin D by pubertal stage.
  
  
  CONCLUSIONS
  Vitamin D supplementation improved bone mass and several DXA-derived structural bone parameters, in adolescent girls, but not boys. This occurred at a critical site, the femoral neck, and if maintained through adulthood could improve bone strength and lower the risk of hip fractures.
authors.affiliation: Calcium Metabolism and Osteoporosis Program, Department of Medicine, Lebanon.
authors.forename: Laila
authors.initials: L
authors.lastname: Al-Shaar
authors.forename: Mona
authors.initials: M
authors.lastname: Nabulsi
authors.forename: Joyce
authors.initials: J
authors.lastname: Maalouf
authors.forename: Rola
authors.initials: R
authors.lastname: El-Rassi
authors.forename: Reinhold
authors.initials: R
authors.lastname: Vieth
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Beck
authors.forename: Ghada
authors.initials: G
authors.lastname: El-Hajj Fuleihan
mesh_terms: D000293:Adolescent; D015519:Bone Density / Q000187:drug effects*; D002762:Cholecalciferol / Q000627:therapeutic use*; D005260:Female; D005269:Femur / Q000187:drug effects; D006621:Hip Joint / Q000187:drug effects*; D006801:Humans; D008297:Male; D010384:Pelvic Bones / Q000187:drug effects
chemical_list: D002762:Cholecalciferol
keywords: Adolescence; Gender; Hip structural analysis; Lean mass; Randomized trial; Vitamin D